Induction heating systems may be required to run from a source of AC mains voltage that is limited by a circuit breaker and yet must deliver the most heating practical to a load. Such systems need high power factor and high efficiency. Further, if volume manufacturing is intended, such systems must be relatively tolerant of changes to the resonant circuit and loading that may occur due to unit-to-unit variations and environmental variations such as in temperature. Further, such systems must be adaptive to changing line voltage and power line “sag” when the application requires a tightly controlled average power or total energy to the load. Additionally, the electromagnetic interference generated by such systems must typically be limited to meet regulatory requirements. Protection for the switching device(s) is generally desired to make the system robust. The technique may also be used to drive an output rectifier and filter for DC load applications as a switching supply.